1. Field of the Invention
The present invention relates to an image correcting method and device for correcting an image displayed on a cathode ray tube (CRT), for example, and a cathode ray tube display unit to which they are applied.
2. Description of the Background Art
FIG. 24 is a block diagram showing an image correcting device according to the prior art. The image correcting device shown in FIG. 24 comprises a CR timer 1, a microcomputer 2a, drivers 3 to 7, first to fourth coils 8 to 11 for correcting landing (which will be hereinafter referred to as landing correcting coils), and a coil 12 for correcting convergence (which will be hereinafter referred to as a convergence correcting coil). The first to fourth landing correcting coils 8 to 11 and the convergence correcting coil 12 are fixed to a cathode ray tube (not shown).
When the cathode ray tube is turned on (the time that the cathode ray tube is turned on will be hereinafter referred to as xe2x80x9cpower ONxe2x80x9d), a deterioration in the landing and convergence of the cathode ray tube starts to be caused. When the cathode ray tube is turned off (the time that the cathode ray tube is turned off will be hereinafter referred to as xe2x80x9cpower OFFxe2x80x9d), the deterioration starts to be recovered. The CR timer 1 always operates also when the cathode ray tube is turned on and off. The CR timer 1 outputs a deterioration detecting signal TS according to the degree of the deterioration in the landing and the convergence.
The microcomputer 2a calculates an optimum correction current value from the deterioration detecting signal TS when a time passes after the power ON. The drivers 3 to 7 cause a correction current having the value calculated by the microcomputer 2a to flow to the first to fourth landing correcting coils 8 to 11 and the convergence correcting coil 12. The first to fourth landing correcting coils 8 to 11 and the convergence correcting coil 12 properly regulate the landing and the convergence according to the correction current.
As described above, the image correcting device automatically corrects the landing and convergence of an image displayed on the cathode ray tube by supplying the correction current to the cathode ray tube.
FIGS. 25 and 26 show a state obtained immediately after the power ON and conventional changes in the landing and the convergence to a state obtained after the time fully passes (for example, three hours) since the state obtained immediately after the power ON. As shown in FIGS. 25 and 26, the landing and the convergence are not deteriorated immediately after the power ON. Therefore, an image is displayed in a desired position (that is, a displacement from the desired position of the image is a minimum (zero)). Thus, a state in which the image is displayed in the desired position will be referred to as a xe2x80x9cjust statexe2x80x9d. The states of the landing and the convergence which are obtained at that time will be referred to as xe2x80x9cjust landingxe2x80x9d and xe2x80x9cjust convergencexe2x80x9d, respectively.
As the time passes after the power ON, the landing and the convergence are deteriorated and the image is shifted from the desired position and is displayed. When the time fully passes (for example, three hours) after the power ON, the deteriorations in the landing and the convergence are brought into a saturation state and the displacement from the desired position of the image becomes a maximum.
As shown in FIG. 25, for example, as the time passes after the power ON, an upper left portion of the image is shifted from the left to the right (in a direction F) from the desired position. In this case, if a proper correction current is caused to flow to the landing correcting coil provided for correction on the upper left portion of the image to move the upper left portion of the image in a direction reverse to the direction F, the just state can be obtained, that is, the image can be displayed in the desired position.
FIG. 27 shows a conventional relationship between a time (an elapsed time) which has passed after the power ON and a correction current and a displacement from a desired position of an image. As shown in FIG. 27, conventionally, the correction current has been increased with the passage of the time in order to keep the just state all the time.
However, after the time fully passes after the power ON, the correction current always flows at a maximum value. Accordingly, there has been a problem in that power is largely consumed when the cathode ray tube is to be used for a long time.
In order to solve the above-mentioned problem, it is an object of the present invention to provide an image correcting method and device capable of reducing power consumption required for correcting an image for a long-time use, and a cathode ray tube display unit.
A first aspect of the present invention is directed to a method for automatically correcting an image displayed on a cathode ray tube by supplying a correction current to the cathode ray tube, comprising the step of monotonously decreasing the correction current more as a time passes after the cathode ray tube is turned on.
A second aspect of the present invention is directed to the image correcting method, further comprising the step of reducing a rate of the decrease in the correction current more as a time passes after the cathode ray tube is turned on.
A third aspect of the present invention is directed to the image correcting method, further comprising the step of causing the correction current to approximate to zero after the cathode ray tube is turned on.
A fourth aspect of the present invention is directed to the image correcting method, wherein an object for automatically correcting the image includes at least one of landing, convergence and a horizontal image position.
A fifth aspect of the present invention is directed to an image correcting device for automatically correcting an image displayed on a cathode ray tube by supplying a correction current to the cathode ray tube, comprising a calculating circuit for calculating a value of the correction current in such a manner that the correction current is more decreased monotonously as a time passes after the cathode ray tube is turned on, a driver for generating and outputting the correction current in accordance with a result of the calculation obtained by the calculating circuit, and a correcting device provided in the cathode ray tube for correcting the image displayed on the cathode ray tube on receipt of the correction current from the driver.
A sixth aspect of the present invention is directed to the image correcting device, wherein the calculating circuit calculates the value of the correction current in such a manner that a rate of the decrease in the correction current is more reduced as a time passes after the cathode ray tube is turned on.
A seventh aspect of the present invention is directed to the image correcting device, wherein the calculating circuit calculates the value of the correction current in such a manner that the correction current is caused to approximate to zero after the cathode ray tube is turned on.
An eighth aspect of the present invention is directed to the image correcting device, wherein the correcting device includes at least one of a coil for correcting landing, a coil for correcting convergence and a yoke for correcting a horizontal image position.
A ninth aspect of the present invention is directed to the image correcting device, further comprising an external terminal for giving data necessary for the calculating circuit to calculate the value of the correction current from an outside.
A tenth aspect of the present invention is directed to a cathode ray tube display unit comprising the image correcting device according to any of the fifth to ninth aspects of the present invention, and the cathode ray tube.
According to the first aspect of the present invention, the correction current is more decreased as the time passes. Consequently, the power consumption necessary for correcting the image can be more reduced as the time passes. Therefore, the power consumption can be reduced for a long-time use.
According to the second aspect of the present invention, the characteristics of the cathode ray tube cause the rate of the increase in the deterioration to be more reduced as the time passes after the cathode ray tube is turned on. Correspondingly, the rate of the decrease in the correction current is more reduced as the time passes. Consequently, the image of the cathode ray tube can properly be corrected.
According to the third aspect of the present invention, the correction current becomes zero if the time fully passes after the power is turned on. Therefore, it is possible to cause the power consumption necessary for correcting the image to become zero.
According to the fourth aspect of the present invention, it is possible to reduce the power consumption necessary for correcting the landing, the convergence or the horizontal image position.
According to the fifth aspect of the present invention, the driver further reduces the correction current as the time passes. Consequently, the power consumption of the correcting device can be more reduced as the time passes. Therefore, it is possible to reduce the power consumption for a long-time use.
According to the sixth aspect of the present invention, the characteristics of the cathode ray tube cause the rate of the increase in the deterioration to be more reduced as the time passes after the cathode ray tube is turned on. Correspondingly, the rate of the decrease in the correction current output from the driver is more reduced as the time passes. Consequently, the image of the cathode ray tube can properly be corrected.
According to the seventh aspect of the present invention, the correction current output from the driver becomes zero if the time fully passes after the power is turned on. Therefore, it is possible to cause the power consumption necessary for correcting the image to become zero.
According to the eighth aspect of the present invention, it is possible to reduce the power consumption of the coil for correcting landing, the coil for correcting convergence or the yoke for correcting a horizontal image position.
According to the ninth aspect of the present invention, the data corresponding to the cathode ray tube is given to the external terminal. Consequently, it is possible to perform optimal correction on the cathode ray tube.
According to the tenth aspect of the present invention, the power consumption of the cathode ray tube display unit can be reduced for a long-time use.